JPH043615B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a vacuum level drop detection device for a vacuum interrupter.

B. Summary of the Invention The present invention is a device for detecting a decrease in the degree of vacuum in a vacuum interrupter equipped with an intermediate shield, which detects the ground potential of the system line and the ground potential of the intermediate shield, and detects changes in the peak value difference of the detection signal. At the same time, when the vacuum level decreases, a discharge occurs between the grid potential member and the intermediate shield on either the fixed side or the movable side before reaching the unbreakable area when the vacuum level decreases. By providing a vacuum gap and configuring the system to detect a decrease in vacuum, it is possible to reliably detect a decrease in vacuum while the vacuum is still high (at the beginning of a leak), and even when the power is on. The vacuum level can be monitored at all times, and it can be turned off even after a decrease in the vacuum level is detected.

C. Prior Art Vacuum interrupters inherently have a longer life both electrically and mechanically than other switching devices, and require almost no maintenance or inspection. However, in addition to a decrease in the degree of vacuum due to an increase in the number of shear breaks, the degree of vacuum may also decrease due to vacuum leakage from bellows, airtight joints, etc., although this is very rare. A vacuum interrupter (current interrupter) has a reduced degree of vacuum, resulting in a decrease in interrupter performance as a vacuum interrupter, and eventually becomes unable to interrupt the interrupter. Therefore, it is required to regularly or constantly check the degree of vacuum. Moreover, it is desired that the vacuum interrupter can accurately and easily test the degree of vacuum in the energized state after being assembled with an operating mechanism to form a vacuum interrupter.

On the other hand, the degree of vacuum of the vacuum interrupter and the discharge starting voltage of the vacuum gap have a relationship similar to Patsien's law, as shown in FIG. In FIG. 5, the horizontal axis shows the internal pressure of the vacuum interrupter, and the vertical axis shows the discharge starting voltage. In the figure, the solid line (partially broken line) m shows the characteristics when the vacuum gap is 10 mm. As can be seen from FIG. 5, if the degree of vacuum inside the vacuum interrupter is a high vacuum of 10 ^-4 mmHg (13.33 mPa) or less, the discharge starting voltage is extremely high. However, when the degree of vacuum deteriorates to around 10 ^-1 mmHg (13.33Pa)
Internal circuit occurs at 500V.

Conventionally, means for detecting a decrease in the degree of vacuum of a vacuum interrupter using such a law is known, and an example thereof is shown in FIGS. 6 and 7.

First, the system shown in FIG. 6 attempts to determine the degree of vacuum by detecting the rise in ground potential of the intermediate shield.

In the figure, 1 is a vacuum interrupter, and 2 is an intermediate shield. This intermediate shield 2 is provided insulated from grid potential members (members having the same potential as the grid circuit) such as the fixed electrode rod 4a and the movable electrode rod 4b. It is being 21 is an impedance, 22 is a detector, and the intermediate shield 2 is connected to the ground via the impedance 21 and the detector 22. 3
a, 3b are auxiliary shields, 40 is a bellows, 41
A and 41b are metal end plates, and 42a and 42b are electrodes. Further, 43 and 44 are an insulating cylinder and a sealing fitting, respectively, and constitute a vacuum container together with the metal end plates 41a and 41b.

In such a configuration, when vacuum deterioration occurs, the insulation between the intermediate shield 2 and the grid potential member is broken, the potential of the intermediate shield 2 rises to almost the grid potential, and as a result, the detector 22 receives electricity. A signal is provided so that a decrease in vacuum can be detected.

Incidentally, in order to improve the withstand voltage characteristics when the contact is opened, vacuum interrupters are generally constructed so that the electric field distribution state is approximately symmetrical between the fixed side and the movable side. That is, the intermediate shield 2, the auxiliary shields 3a and 3b, and the metal end plate 4.
1a, 41b, etc., the fixed side and the movable side have the same size gap.

For this purpose, in the means shown in FIG. 6, the fixed side and the movable side are constructed symmetrically as described above, so that the intermediate shield 2 and both the fixed side and the movable side can be connected at almost the same degree of vacuum. discharge occurs in each case. Therefore, even if a decrease in the degree of vacuum is detected in a vacuum region that can be cut off and the operating mechanism (not shown) is activated to open the electrodes 42a and 42b, the fixed side and the movable side are connected via the intermediate shield 2. Since there is an internal circuit between the two, the current cannot be cut off.

In addition to these problems, since the detection is based on the potential rise of only the intermediate shield 2, in order to avoid the influence of voltage fluctuations in the grid circuit, it is necessary to keep the ground potential _E3 of the intermediate shield 2 almost at the grid potential. It must be detected when the temperature rises to _E1 . Therefore, at the time when a decrease in the degree of vacuum is detected, the degree of vacuum has already decreased to such an extent that even the rated load current can no longer be cut off.

In addition, the one shown in FIG. 7 opens the electrodes 42a and 42b, applies a voltage in that state, and compares the voltages to determine whether or not the degree of vacuum has decreased (Japanese Patent Publication No. 114-1982). (see official bulletin).

That is, in the figure, C _V is the capacitance of the vacuum interrupter in the open state, and C _A and C _B are the ground capacitances of the fixed electrode rod 4a and the movable electrode rod 4b, respectively. Now, if vacuum interrupter 1 is in an open state and ground voltage Eo is applied to it, the terminal voltage Ea between a and e is Ea = Eo, and the terminal voltage Eb between b and e is Eb = C _V /C _V +C _B becomes Eo. That is, Ea>Eb. However, if the vacuum interrupter 1 has a vacuum failure, an arc discharge occurs between a and b, resulting in conduction. Moreover, since the arc voltage in this case is several tens of volts or less, which is sufficiently small compared to the applied voltage Eo, it can be considered that Ea≈Eb. Therefore, when the vacuum interrupter is open, it is normal if Ea>Eb, and Ea≒Eb
If so, it can be determined that the vacuum is defective. In practice, each terminal voltage is measured using a capacitor voltage divider for safety reasons.

However, this method has a problem in that it is impossible to constantly monitor the degree of vacuum while electricity is being applied because the detection is performed in an open state.

By the way, the state in which the techniques shown in FIG. 6 and FIG. 7 are combined, that is, in FIG. 6, not only the potential of the intermediate shield but also the grid potential is considered, and based on both the intermediate shield potential and the grid potential, An attempt was made to determine the degree of vacuum.

In other words, by taking the grid potential into consideration and detecting the intermediate shield potential using this as a reference, it is attempted to eliminate the adverse effects of voltage fluctuations.

However, even with this, the sixth
A similar problem arose as in the case of the means shown in the figure. That is, since the fixed side and the movable side are constructed symmetrically, electric discharge occurs between the intermediate shield 2 and both the fixed side and the movable side at approximately the same degree of vacuum, causing the electrodes 42a and 42b to Even if the poles are opened, a flashover occurs between the fixed side and the movable side via the intermediate shield 2, and the current cannot be cut off.

D Problems to be Solved by the Invention As described above, in the conventional technology, as the degree of vacuum decreases, flashover occurs between the intermediate shield and both the fixed side and the movable side at approximately the same degree of vacuum. The load current cannot be cut off even if a drop is detected.
In order to avoid the effects of voltage fluctuations, the detection voltage must be set high, and when a drop in the vacuum level is detected, the vacuum level cannot be cut off any longer, and there are problems in that the vacuum level cannot be constantly monitored while the power is on. Ta.

The present invention has been made to solve these problems.

E Means for Solving the Problems The present inventors studied the discharge phenomenon in a vacuum interrupter and obtained the characteristics shown in FIG. 4. FIG. 4 shows the vacuum interrupter internal pressure on the horizontal axis and the discharge starting voltage on the vertical axis. In FIG. 4, solid line m ₁ , solid line m ₂ and solid line m ₃ indicate the characteristics of vacuum gaps A, B and C, respectively, and have a relationship of A>B>C.

In general, it was known that long gaps have a higher discharge starting voltage than short gaps, but as can be seen from Figure 4, this phenomenon occurs in high vacuum or near atmospheric pressure, and is 10 ^-2 mmHg. In the region around (1.333 Pa), on the other hand, the discharge start voltage is higher in the short gap than in the long gap. The short gap had sufficient withstand voltage in the region of around 10 ^-2 mmHg (1.333Pa).

Based on this knowledge, the present invention first provides a metallic intermediate shield insulated from the electrode, and creates a space between the intermediate shield and the system potential member on either the fixed side or the movable side to reduce the degree of vacuum. A vacuum gap is formed that discharges in a vacuum region that can be cut off at any time. Then, a first impedance and a second impedance are provided between the grid potential members, for example, between the grid line and the ground, and between the intermediate shield and the ground, respectively, and further, the ground potential of the grid line obtained through the first impedance. A determination unit is provided which compares the peak value of the detection signal of the detection signal and the detection signal of the ground potential of the intermediate shield obtained via the second impedance, and determines whether the degree of vacuum has decreased based on the difference in peak value.

F. Effect When the degree of vacuum in the vacuum interrupter decreases during energization, discharge begins at the long gap provided on either the fixed side or the movable side before reaching the uninterruptible region. At this time, no discharge occurs in the other vacuum gap (short gap), and the short gap is not induced to discharge by the discharge in the long gap. On the other hand, by discharging with a long gap, a fluctuation occurs in the wave height difference between the ground potential of the grid line and the ground potential of the intermediate shield, and as a result, a decrease in the degree of vacuum is immediately detected by the determination unit. Since it is detected when only the long gap is discharging, the current can be quickly cut off by opening the electrodes immediately after that.

G Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an equivalent circuit of the circuit in FIG. 1. The same reference numerals in FIG. 7 indicate the same parts. In this embodiment, the axial length of the auxiliary shield 3a is made small, and the end of the intermediate shield 2 on the fixed end plate 41a side is made to protrude sufficiently longer than the end of the auxiliary shield 3a in the axial direction. Part is auxiliary shield 3
The fixed electrode rod 4a is directly opposed to the fixed electrode rod 4a through a gap without sandwiching the electrode rod 4a. The gap length l of the gap is a length that allows discharge in a vacuum region that can never be cut off when the degree of vacuum decreases, and is the maximum distance between members of different potentials in the vacuum interrupter 1.

Note that when electrons fly between members with different potentials, they fly in a direction perpendicular to the equipotential lines, so the distance described here means the flight distance of the electrons. In the figure, 4b is a movable electrode rod.

5 is a first circuit that detects the ground potential _E1 of the grid line.
The impedance voltage divider is provided, for example, in the vicinity of the vacuum impedance 1 between the power supply side electric circuit and the ground. The first impedance voltage divider 5 is composed of impedance components Z ₁ and Z ₂ such as capacitors and resistors.

6 is a second impedance voltage divider for detecting the ground potential E ₃ of the intermediate shield 2, and is composed of capacitors C ₁ and C ₂ having a capacitance of 0.1 μF and 100 pF, respectively. Note that the second impedance voltage divider 6 is not limited to using a capacitor.
Furthermore, the connection between the intermediate shield 2 and the fixed electrode rod 4a of the vacuum interrupter 1 is represented by a parallel circuit of a capacitor _C3 and a resistor R, as shown in Fig. 2, and the capacitance of the capacitor _C3 when closed is 20 pF. It has a magnitude of ~100pF.

7 is a determination unit, and this determination unit 7 determines the respective peak values of the detection potential e ₁ detected by the first impedance voltage divider 5 and the detection potential e ₃ detected by the second impedance voltage divider 6. Wave peak value hold circuits 71 and 72 to hold, and this hold circuit 7
A differential amplifier 73 that amplifies the output difference from 1 and 72.
and a comparator circuit 74 that issues a judgment signal, such as an alarm, for a decrease in the degree of vacuum when the output signal from the differential amplifier 73 falls below a predetermined value.

Next, the operation of the above embodiment will be described.

The ground potential of the grid circuit and intermediate shield is
The detected potentials e 1 and e 3 are detected by impedance voltage dividers 5 and 6, respectively, and the detected potentials e ₁ and e ₃ are respectively detected by peak value hold circuits 7.
1,72. When the degree of vacuum is normal, there is a predetermined peak value difference between the detected potentials e ₁ and e ₃ , and the differential amplifier 73 outputs a signal corresponding to the difference. At this time, the comparator circuit 74 does not output a determination signal for lowering the degree of vacuum. When the degree of vacuum decreases now, discharge begins in the gap between the intermediate shield 2 and the fixed electrode rod 4a. As for the reason,
In the area around 10 ^-2 mmHg of the Patsien curve shown in Fig. 4, the discharge occurs from a point where the gap length is large, and the gap length l is
Since this is the maximum distance between members of different potential within the vacuum interrupter 1, local discharge begins at this gap. As a result, the potential of the intermediate shield 2 changes, and the peak value difference between the detected potentials e ₁ and e ₃ changes, and if the change exceeds a predetermined value, the comparator circuit 74 outputs a judgment signal for reducing the degree of vacuum. be done. FIG. 3 is a waveform diagram of each detected potential when the degree of vacuum decreases.

In the above-mentioned embodiment, a gap having the maximum distance is provided between the fixed electrode rod 4a and the intermediate shield 2, but in the present invention, in order to avoid flash shorting on the fixed side and the movable side, the gap is provided between the fixed electrode rod 4a and the intermediate shield 2. If it is either one of the movable sides, it is not limited to the electrode rod, but the metal end plate 41
A vacuum gap may be provided between the system potential members such as a and 41b and the intermediate shield 2, which discharges in a vacuum region that can be cut off when the degree of vacuum is reduced. In the present invention, detection can be performed not only in the closed state but also in the open state, and in this case, it is necessary to provide the gap on either the fixed side or the load side, which is the charging part side.

H. Effects of the Invention As described above, according to the present invention, a discharge occurs between the intermediate shield and the grid potential member on either the fixed side or the movable side in a region where the degree of vacuum is reduced and it is possible to Since a vacuum gap is formed, an electric discharge occurs on either the fixed side or the movable side at the beginning of a leak (high vacuum) when the degree of vacuum decreases. At this time, the other vacuum gaps have sufficient withstand voltage.
Moreover, the configuration compares the detection signal of the ground potential of the grid potential member and the detection signal of the ground potential of the intermediate shield in terms of peak value, and detects a decrease in the degree of vacuum by detecting the change in the peak value difference, so the voltage of the grid electrical circuit is It can be detected at the stage of local discharge due to a decrease in the degree of vacuum without being affected by fluctuations or weight noise. As a result, it is possible to detect the initial stage of a leak due to a decrease in vacuum level, so it is possible to respond in a vacuum range with a higher withstand voltage than the working voltage range (voltage that can be interrupted), but the leak may occur after detecting a decrease in vacuum level. be able to. Furthermore, since a decrease in the degree of vacuum can be detected in the closed state, the degree of vacuum can be constantly monitored while electricity is being supplied.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit to the circuit in FIG. 1, FIG. 3 is a waveform diagram showing detected potentials from each impedance detector, and FIG. The figure is a curve diagram showing the relationship between the degree of vacuum and the discharge starting voltage between the gaps when the vacuum gap is different, Figure 5 is a curve diagram showing Patsien's law, and Figures 6 and 7 are each for conventional vacuum degrees. FIG. 2 is a principle diagram showing the principle of a drop detection device. DESCRIPTION OF SYMBOLS 1... Vacuum interrupter, 2... Intermediate shield, 3a, 3b... Auxiliary shield, 4a... Fixed electrode bar, 4b... Movable electrode bar, 5... First impedance voltage divider, 6... Second Impedance voltage divider, 7... Judgment section, 71, 72... Peak value hold circuit, 73... Differential amplifier, 74... Comparison circuit.

Claims (1)

[Scope of Claims] 1. A vacuum container is formed by closing both ends of a cylinder with end plates, and a fixed electrode rod is airtightly introduced into the vacuum container from one end plate, and a fixed electrode rod is inserted from the other end plate. A movable electrode rod that can be moved toward and away from the electrode is airtightly introduced through a bellows, and a pair of fixed and movable electrodes that can be moved toward and away from each other is provided at each inner end of these electrode rods, and at least the above-mentioned In a device for detecting a decrease in the degree of vacuum in a vacuum interconnector that can freely open and close a power grid circuit, the intermediate shield made of metal surrounding the outer periphery of an electrode is insulated from the electrode, and the intermediate shield is connected to either the fixed side or the movable side. A first impedance is provided between the grid potential member and the ground, forming a vacuum gap that discharges in a vacuum region that can be disconnected when the degree of vacuum is reduced, and the grid potential member and the ground. , a second impedance provided between the intermediate shield and the ground, a detection signal of the ground potential of the grid potential member obtained via the first impedance, and the second impedance.
A determination unit that compares the detection signal of the ground potential of the intermediate shield obtained through the impedance with respect to the peak value, and determines whether or not the degree of vacuum has decreased based on the difference in peak value. Temperature drop detection device.